Diversity combiner



May 18, 1948.

EECE/I/Efl OUTPUT //V 08 (RECEIVE/3 B M. G. crosew 2,441,661

DIVERSITY COMBINER I Filed A rilzo, 1943 e Sheets-Sheet 1 srmvonleo 0(VEA? S/TY I Wcamewae CHEB/EB INPUT //V 05 INVEN TOR. mrmz 6. Crosby ATTORNEY May 18, 1948.

M. s. CROSBY I DIVERSITY COMBINER Filed April 20, 1943 6 Sheets-Sheet 2 Hung 6. Orosiwy BY Arron/my May 18, 1948.

Filed April 20, 1945 6 sheets sheet 5 F I ,508 "20s f-F fl/VPL/F/EB EECE/VEB 82 I-F FROM BECE/YEB *2 DETECTIED IF INVEN TOR.

6. Crosby BY ATTOBNEY May 18, 1948.

M[G.CROSBY DIVERSITY COMBINER Filed Apr i1 '20, 1945 6 Sheets-Sheet 4 Z6 FROM A TTOIZ/VEY May 18, 1948. M. G. CROSBY 2,441,661

' DIVERSITY COMBINER Filed April 20, 1943 6 Sheets-Sheet 5 i 4 a AMPLIFIER llllllll IIIIII'I ITNVENTOR. library 6. Crosby ATTORNEY May 18, 1948.

ese TIP/ED oureur k HERE DIODE DE TEC 70B COMB/NED IF; FEOM flLL 3 EEC.

llllllll M. G. CROSBY DIVERSITY COMBINEB Filed April 20, 1943 6 Sheets-Sheet 6 n-c coma/N150 COMB/NEE //v our 5 llllll .1. T P0 WEB SUFPL Y II I FILTERS all 1 a" IF FBOM -L INVENTOR. M'ur nay A TTOBNEY 6. Crosby I of the available receivedssignalsziq utilization Patented May 18, 1948 Mun-an G.. Crosb t Kiwi-head; N- Y., alss'i'gjici i to, Radio commuted meti'ca, a. e'tnieratien ot l laivare Applic ationeApril; 2 ll,

It: is also knoWnin-theart togproyide;afliyeyeitx;

receiving system. with selecting 0 E switszh ng means vfor automatically selecting. only the b st the common. output. circuit. 'Ikhisi. leleotiun done continuously with negligible delay; while; atathe same time those receiuersl-whichhailele: cei'ved feeble or unsatisfactory signals are i;- fectively; disassociated: from the: eommonu tiOlLxCiIfCllit. Reference-isJmade to:United; St.., es: Patents=2,25'3,867-and;2,290;392; granted tQJHfiIOj-di O.- Peterson-on August 26; 1941., and; July 28; 19,42; respectively, asexamples ofv theprior art, 7

The present invention. is; a diversity receivin system having a more sensitive: eleotron-wswit hi-l ing. system forrapidly;-and. lautomatiqally; select:- ingsthe best receiver out ;of theagroup feedingthe, common utilization circuit. The improved: 11eceiver selector circuitof the invention automatincally selects the strongest signal and't reduces ;,the; probability of more than a. single IeQeiYeIEfiIDa; diversity system contributing to the common outer: put circuit at one time. This is done, Lem-gene. erally speaking, by controlling 111.1103/6111'1'13111131'. the amplification of the channelsfedby. the sepa: rate-receivers; It has been proven that; the possibilitylof theidetectedcoutputs flOmLiJWOJZBQQfifi cancelling. each other and producing distortion in,

the com'mon output circuit; duning. the=.cross.-maer;

period in whichtwo-varying'.:signalszfromfliffierehtz receivers in- 'the same diversity system pass through equality, is lessinzthe system olfithepzliese ent' invention; than in: rionsystems l Another advantage ofinth'e invention. lies thefact that the very; fashswitching; action of; thesjreoeiver selector: permits, the diIeo.t.. Q0mbin-afziDn -i il the intermediate: irsque @11 h trt e. sepa ate si na s :m 1. eminent te ce yensi 'Ncrmeilnwhen: this- .1 ime he 1341* 194s, SeriabNo.4&3;741

ost tz ria fqns; in chase t. he carriers i. hesep k vfie; s n ls. eu'se the to; alternat ngi' aid} so: that. no improvement re: 'I 'heusua 1 diVIe1IS yis buc in nd idin W directecutr ntr o'r. eeexeemh i e h alterna r ns; limate f em the: eifieree W n fih e l. V in ew terme.,,a;t e ney erierest which,. i's .at e a li eat n es a e mthe strongest signal. Where; the: c v a A rfi ll nfi h 1 ml .2 em t usen impl ated hat are; o h a sii l e nterm ia e re d uce' wi l' l h nv ntion 2 i of the duplic'atioihwhiph. e equ d we each. diil rsifi r is si nteee ss tq ely; feltinl the Y eeueee nerg e l i r t e iie eamede i di e th cas e of a three itee Al u e if-su h sem ninetzinec exeenee v,it N h Yentipn mouldinquireten y ne-finit aeieisr mm i ee 3Q of three.

H method: Qt Qemb nine the tp t /oi the me ideal n se ersi .hittlieeembiee ed he it the rectifiersr mrstgonger: signal to, place a d resistor o; such av theweaken d. r nt 49 Qensequ totheo tp nera enf the stra erca r ime as str ee e hemes ee s e lie b eker semen it t e-em hen. meses tt ne as. h

Ame e innlete es ie be of t e n ntion el owsinsept m-e9 W ihe l henein; 1 1 e i .1 vgrabbi.ta llustxates, o qomnarison men es, he inputroutuutl.Qhara ter st oi. h Q indivi ual'treeeiye. of a diYfilfSity syst m.

ns is eliminated} However," such 1 w thh rit s-@ utput on sts of. a;

n ts; ll he; he nte media e e or a uener me e e th This, causes the ts h ve indicated-,lthatth other embodiment of a diversity receiving system in accordance with the invention; and Figs. 4a and 4b taken together illustrate in detail the selector of Fig. 32) for selecting the receiver having the strongest signal. Fig. 1 shows an experimentally determined of combiner of the present invention. curves were taken on a two-receiver diversity system which was fed carriers which were amplitude modulated by different tone frequencies. The carrier fed to one receiver A or B was modulated by a 1350 cycle tone and that fed to the other B or A by a 1785 cycle tone. These tones were separated in the receiver outputs by means of audio filters. Hence the amount of output contributed by one receiver could be determined by measuring the amplitude of the tone on the carrier fed to that particular receiver. In this way, the carrier amplitudes were relatively varied and the amount contributed to the output by each receivermeasured. The solid line curves were taken on the conventional diversity combination to furnish a basis of comparison. The dotted line curves were taken with the receiver selector switched in, following the principles of the present invention. It can be seen that the switch-over of the outputs from the diiferent receivers of the same diversity system for a given change in inputs is much more rapid for the condition in which the combiner was used. For example, when the carrier input for the two receivers of the conventional system corresponded to 1 decibel, the difference in output of receivers A and B amounts to only 28.826.4, 'or 2.4-decibels. By switching the carrier input 'to produce a +1 decibel input, the difference in output of the same two receivers in the conventional system is 28.8 26.8 or 2.0 decibels. Howevenwith the'system of the invention, referring to the dash line curves, the differences in outputs of the two receivers for both 1 decibel input and +1 decibel input are, respectively, 3l.09.5 or 21.5 decibels and 28.8-12.8 or 16 decibels.

In Fig. 2, which shows diagrammatically one embodiment of a diversity receiver in accordance with the present invention, there are three receivers of the superheterodyne type having the-- same apparatus in each of the receivers. The same units in the different receivers have been given the same reference numerals with prime designations added. The three receivers each include an antenna A, A or A". Each antenna is arranged to feed the collected signal energy into its own radio frequency amplifier B, B or B". The output from each of these radio frequency amplifiers is fed to an appropriate frequency converter C, C" or C". Y A common heterodyne oscillator O feeds energy into the frequency converters of the three receivers in order to produce intermediate frequency energies which are amplified in intermediate frequency amplifiers D, D and D. Since all three receivers receive the same radio wave and employ a common heterodyne oscillator, it will be evident that the intermediate frequency energies in all three receivers are synchronized in frequency. The ,outputs from the intermediate frequency amplifiers are fed to transformers I, I and I". Inasmuch as all three channels of the diversity receiver are similarly equipped and similarly labeled, except for the prime designations, and operate similarly, a description of only one of the channels provides a description of the operation of the other two channels. Considering the uppermost channel in the drawing as representative of all three channels, there is shown a control amplifier stage comprising a pair of pentode amplifier tubes 3 and 4 whose control grids G and G, respectively,

are connected together in cophasal relation through a blocking condenser I l, but whose outcurve which portrays the operation of the .type

These put or..anode.electrodes A and A, respectively, are connected in out-of-phase relation to the opposite terminals of a parallel tuned circuit i2 whose inductance forms the primary winding of i a transformer 61 It will thus be seen that the control amplifier stage 3, 4 has a push-push input circuit and a push-pull output circuit, and that this control amplifier will not amplify when there is no direct current bias fed to either of the two control grids. The control grid G of tube 3, it should be noted, is connected to the upper terminal of a parallel tuned circuit I3 whose inductance coil forms the secondary winding of the intermediate frequency transformer l. At this time it should be understood that the parallel tuned circuit whose inductance coil forms the primary winding of transformer l is tuned to the same frequency as the secondary tuned circuit l3, which is the intermediate frequency passed by the transformer l. The control grid G of tube 3 is also connected to the anode A of a diode rectifier 2 whose cathode is connected in common to the cathodes of the other diode rectifiers 2' and 2" of the other receivers. The lower terminal of intermediate frequency tuned circuit I3 is connected to a resistor-shunt condenser combination l 0. The output of the control amplifier stage 3, 4 is coupled through transformer 6 to a pentode amplifier vacuum tube 5, the latter in turn feeding energy via a transformer I to a diode rectifier 8. At this time it should be observed that the input and output circuits of both the control amplifier stage 3 and the succeeding amplifier stage 5 are tuned to the same intermediate frequency. The energy rectified by diode 8 appears across a diode resistor 9, the latter being shunted by a suitable condenser. This diode resistor 9 in the cathode circuit of diode 8 is common to all of the diodes 8, 8', 8" of all of the channels, and has its upper terminal E connected by way of lead M to the cathodes of the diode rectifiers 2, 2', 2" of all three channels. In view of this arrangement, itwill be evident that the rectified output of the entire system, consisting of the detected audio frequency or telegraph voltages, appears across the common diode resistor 9, and is fed over lead IE to a suitable utilization circuit which can be a loudspeaker, headphone or recorder, depending upon 'thetype of signals to be received by the diversity system.

A description of the operation of the system of Fig. 2 now follows: Let it be assumed that the signal received from that receiver 1 comprising the uppermost of the three receivers of Fig. 2 is the strongest. This signal passing through transformer I will cause rectifier 2 to draw current and cause rectified voltage to be applied to the'control grid of tube 3. The control grid of tube 3 will be biased negative by the rectified voltage built up on resistor of circuit l0 due to the incoming signal being rectified by the diode 2, and thus upset the balance in the control amplifier 3, 4 and-permit the intermediate frequency coming currents.

. 5 signal energy to be passed from the control amplifier to the transformer 6. The'bias on the control'grid G of tube lof the amplifier always remains fixedfby virtue of the fact'that it'is connected to ground through a fixed resistor '48 and does 'not obtain voltage from the transformer I on" account of'the'location of the blocking condenser H. The resultant amplification of the intermediate frequency energy in the control amplifier stage "3, 4 causes energy to be fed over transformers andamplifier '5 and transformer 1 tojthe' diode 8. Diode Brectifies the energy impresse'd'thereon and the resultant rectified voltage appears on the common diode resistor *9; This rectified voltage has an amplitude whose instantaneous magnitude'varies in accordance withthe amplitude of thecarrier'signal impressed on the transformer I. Lead l4, which'is connected to the upper'terminal E 'of the diode resistor 9, supplies apositive voltage to, bias the other diodes 2' and 2", such that no current is drawn by these other diodes, itbeing assumed that the strongest carriersignal or bestavailable signal appears on transformer l. lt'should be noted; therefore, that the strongest signal in one ofthe channels has been employed 'to bias the other channels in'such manner'that they do notfpass current. The biasingof the diodes 2' and 2" of the other two channels (supplied withweaker signals) in the manner "described above, maintains the control amplifier "stages 3,4' and 3", l" of the other 'channels'in'a -balanced condition, sothat they do not passcurrent. It will thus be evident that the strongest signal in anyone receiverturns on its own amplifier stage to pass the intermediate frequency energy and biases the diodedevices controllingt'he'otheramplifier'stages in the other receiver channels, so thatthese last diodes do not drawjthe current necessary to rendertheir associated control amplifier stages responsive toin- The result is a sharp andirepeated switching action that'efiects a very appreciable reduction'in relative intensity ofjthe weaker signals.

. When any two signals in two receiversof the "diversity transmitter ofiFig. 2are of exactly equal strength, both ofthe signals will contribute out-- put to the common diode resistor 9 for utilization over lead 15. Howeventhe percentage'of time that'such a'conditionoccurs, where two signals 'in two receiversare exactly equal, is very small since the probability of two. signals remaining equal in different receivers is small.

*Figs. 3a and 3btaken' together illustrate another embodiment of the present invention, which contains a receiver selector of the type f described in Fig. 2, togetherwith'additional fea- "tures. The seleotor'for thereceiver 'having'the strongest signal is shown in Fig. 3b in box'form. "The'details'of this receiver selector appear in Figs. "4a and 4b taken together, to be described later.

In Fig. 3a thethree receivers of the diversity system are labeled receivers #1, #2, #3 and are each shown in box form, it being assumed that each of the receivers is of the superheterodyne type and that all receiversemploy a common heterodyne wosc'illatorso that the intermediate frequency energies are synchronized in frequency,

as previously described in connection'with the system of Fig. 2. Only those portions .of the channels of the three receivers are shown in Fi .3

whichare necessary'for an understanding of the pe'ration of the present'"invention. The 'same Aapparatus on all'three channels hasj'been'given "the'same reference 'numerals'with theaddition 6 of prime designations to distinguish one channel from another. Taking'receiver #1 for example, whichcontains thesame apparatus as the other receivers,'the intermediate frequency energy is supplied vialead 200 to the control grids ofthe two intermediate frequency amplifier pentode tubes 2! =and202. 'The output from tube '20l passesthrough transformer 203 and appears at termi'nals'flll and "208. The intermediate frequency energy-"passed by amplifierZUZis passed through transformer' lfl l, rectifiedby diode 205, and the rectified or detected intermediate "frequency energy appears on terminal 20b. The intermediate frequency energies and the detected intermediate frequency energies of the othertwo receivers also-appear'on the similarly numbered terminals having the added "prime designations. The intermediate frequency energy from the three receivers appear respectively on terminals H, I; 'M,-N; and 0,? of the receiver selectorcircuit- Fig. 3b. 'Therectifi'edor detectedintermediate frequency energies'from thefthree receivers are transferred to terminals 'S,'T and U, respectively, of the receiver selector circuit. The arrows on the leads connecting the three receivers to the different terminals oftheselectorillustrate the direction in which currents flow fromthe receivers to theselector circuit. The receiverselector is also supplied with a terminal' Q in which appears the combined intermediate frequency energies from all three receiversand-which combined intermediate frequency-energy is passed on tofre- *quency modulator or phase modulator detector 100 shown in box form only. This frequency r modulator or phase modulator detector 100 may "detected outputover a transformer 102 to a jack 2H for utilization by suitable 5 apparatus.

A signal control panel, indicated in box form and labeled Hi3, contains three signal strength indicating milliammeters 1-04; lilfiand it for the three different receivers. "-Thesethree milliammeters are connected-at one; end to a common resistor 2l2 and at this-same end to a lead l5 extending to strappedterminals Jj-Kand L of the receiver selector, While the other terminals of the m'illiamme'ters I 04, 105, Hi6 are respectively connected to terminals "-V ,'--W and X of the receiver selector. The output from the common resistor 2l2istaken from a jack'2l3 which may 'lead to a suitable audio frequency amplifier tone keyer or to a recorder "forfutili'zingamplitude modulated or telegraph type signals.

Before proceeding with a more detailed description of the receiver selector of-Figs. -4a and 4b, it will be evident from what has'been said above in connection with'Figsfi3a and 3b that the system and receiver-selector of l igs. 3a and 3b make available threekinds of output: first, the combined rectified currents which are combinedor utilized for selecting'the receiver having the strongest signal. This is primarily useful in the diversity reception of telegraph and amplitude modulated signals, and provides an output i'n-iack 2l'3. The circuit of the: receiver selector for obtaining this kind of 'output is si'milarto that of Fig. 2, as will appear later. Another kind of rectified output and which is available in jack 2II is that obtained by combining the three intermediate frequency signals and rectifying the combined intermediate frequency signal energies. A third output is a single intermediate frequency output which is representative of the strongest signal and which may be fed to a limiter and discriminator for frequency or phase modulation detection; or fed to a carrier exalted amplitude modulated de: tector where amplitude modulation is employed. This last output is available for utilization at jack MI.

The details of the receiver selector circuit of Fig. 31) (illustrated diagrammatically in box form therein) are shown in Figs. 4a and 4b. Figs. 4a and 41) include three channels having the same apparatus in all three channels, suitably interconnected. The same elements of all three channels have been given the same reference numerals, except for the addition of prime designations to distinguish the channels from one another. The various terminals which appear in the box representing the receiver selector of Fig. 3b are indicated in Figs. 4a and 41).

Each channel of the receiver selector of Figs. 4a and 41) includes a pair of terminals H, I, or M, N, or O, P, across which the intermediate frequency output from one of the receivers of the diversity system appears. Each channel includes a control amplifier stage having a pair of tubes 50 and 5I whose control grids are connected together cophasally by way of condensers 82 and 82' and whose anodes or output electrodes are connected together out of phase by means of a parallel tuned circuit 52. An inspection of the circuit of the control amplifier stage 50, 5I will show that it has a push-push input and a pushpull output and is similar in its essential respects to the control amplifier stage of each channel of Fig. 2. The tubes 50, 5! are normally balanced so that a direct current voltage on the grid of tube 50 is required to cause the stage to amplify. The balance of the two tubes 50 and 5| is set by means of potentiometer I3. This potentiometer varies the relative values of the screen voltages on the two tubes so that their amplification may be made equal. The balance is set by closing switch 8I and adjusting I3 so that there is no signal passed through the output transformer 53. The switch 8| is provided to temporarily switch off the controlling voltage during the adjustment of potentiometer I3 for the balance of the tubes. The controlling voltage from diode 63 is built up across resistor 85 which is bypassed (for intermediate frequency) by condenser 36. This control voltage is fed through resistor 84 (which forms a time constant circuit with condenser 80) through resistor 83 to the grid of tube 5|. Condenser 82 prevents the controlling voltage from getting to the grid of tube 59. The controlling potential is a direct current which will not pass the blocking condensers 82 and 82. The output of the control amplifier stage 50, 5! passes over a powdered iron-core transformer 53, designed to pass the operating frequency, to a pair of amplifier tubes 54 and 55. It should be noted that the control grids of the two amplifier tubes 54 and 55 are connected together and to the tuned circuit comprising the secondary of the transformer 53. The output of amplifier 54 feeds the double diode stage 56 over transformer 51. Amplifier tube 55 has its anode circuit connected in common to the anode circuits of the amplifier tubes 55'- and 55" of the other two channels over leads 58, 58', and 58". The intermediate frequency energies appearing in leads 5B, 58' and 58" of thethree channels combine in lead 59, which is connected to a tuned circuit including the primary winding of transformer 60, from which the combined intermediate frequency energies appear at terminal Q for utilization by apparatus I00 of Fig. 3b, described before. a

The intermediate frequency appearing in transformer 51 of channel I is rectified by the diode detector 56 and the resultant rectified energy appears in lead 6I connected to terminal 10. The rectified intermediate frequency energies from channels 2 and 3 appear in leads GI and 6|", which in turn are connected to terminals I0 and 10". A switch 49 serves to connect terminals V, W and X to which the signal strength indicating milliammeters are coupled, either to the terminals l0, l0 and 10" in one position, or to terminals S, T and U in its other position.

The combined intermediate frequency energies from all three receivers appearing in intermediate frequency transformer 60 are rectified by 'diode stage 62 and the resultant rectified energy appears across terminal R. Thus, it will be seen that the detected outputs of the combined intermediate frequency energies is made to appear across terminal R, in turn connected to the audio frequency amplifier 2I0 (note Fig. 3b). The detected output of the combined intermediate frequency energies is also fed via lead I5, to the right hand terminals of switch I59. Switch I50 can be thrown either to the right to connect the output of rectifier 62 via lead l5" to the channel controlling rectifiers 63, 63 and 93", or can be thrown to the left to connect the channel controlling rectifiers B3, 63', B3" to the common resistor 2I2.

From the foregoing, it will be evident that the different types of output obtainable from the receiver selector are determined by the positions of switches 49 and I50. Let it first be assumed that it is desired to obtain the alternating current combined output from combining post Q. To achieve this, switch 49 is thrown to the left so that the meters in the signal strength control panel indicate the currents from diodes 55, 55 and 56'', which in turn is an indication of the strength of the individual signals which go to .make up. the alternating current combined output. Switch I50 is thrown to the right to connect the output of rectifier 62 to supply the control bias over lead I5" for the channel controlling rectifiers 63, 63 and 63". If, on the other hand, it is desired to obtain a rectified output of the alternating current combined intermediate frequency for utilization from terminal R to amplifier 2|0, the position of the switches 49 and I50 isthe same as before; that is, switch 49 is thrown to the left and switch I50 to the right. If it is desired to observe the direct current com-- bination of the rectified outputs of the individual channels -of.the receiver selector, switch 49 is then thrown to the left to connect diodes 55, 56' and 56" to the signal control panel meters and common diode resistor 2I2. The output is available at jack 2 I3. Switch I50 in this case is thrown to the left so as to obtain the controlling bias for the channelrectifier 63, 63' and 63 from the common rectified outputsof diodes 55, 56' and 56.". The receiver selector may be switched out of the circuit, in order that the conventional diversity receiving combination may be obtained -9. merely by throwing switch it to theright; Con.- nsptiees i e fitath ht e sse eh the intermediate; ireqiiencit diod outputs of" the individual receivers, obtained;fromtterminal'posts Zllfilflfi, and 2065" or the. receivers. toithe si'gnal control panel. from jack 2J3.

Whatisclaimedis;

1. A diversity receiving. systemhaving, a pluralityof; receivers, coupled toidifierent and spaced antennas,acommonheterodyne oscillator coupled to said receivers forenabling said, receivers. to produce-- intermediate frequency outputs, of( the same frequency, separate amplifier s'tagescoupled to the intermediate frequency- "outputs of; said. re,- ceivers, eachof said amplifier.) stages having a push-push input circuit and a'push-pulloutput circuit, a first rectifier coupled, to the puslirpllsh input of each'of said amplifier, stages'meansconnecting together the cathodes oi all of, said: first rectifiers, a second. rectifier coupled-tothe pushpull output of each of said amplifier stages;- each of said rectifiers having a cathode, electrode, means connecting together the cathodes of said second rectifiers, a common, output' .resistor. for saidssecond rectifiers; and a connection. from. said resistor extendingback tothe cathodes, of. said first rectifiers: to; supply a bias thereto upon the appearance of rectifiedioutput voltageacrossthe resistor.

2. A- diversity receiving system, having a plurality of receivers of the superhetero'dyne type coupled to different and. spacedfantennas; the output of each receiver representing afchannel for said system, a commonheterodyne' oscillator for-said receivers, a controlfamplifier coupled to the intermediate frequency output of each receiver, said control. amplifier having. a pair of vacuum tubes whose control grids'aife, connected together through a condenser for pushrpl'lshoperation and whose anodes are coupled to opposite sides of a parallel. tuned circuit for push-pull operation, a diode forv each control amplifier, said diode having-an 'anodecoupled directl'yto the control grid. of one of. said; pair. of -tuhes, "a

rasa a-th il i l i s a e a resistor connecting the-control grid'of'thejother tube to ground, direct current conductive connections between, the cathodesrof all of, said diodes, each. diode" having a resistor individual thereto, a rectifier "coupledto the-output of each control amplifier, direct connections between thecatl'io'des oi the rectifiers of. saidchannels afcommon out.- put resistorfor allfof saidl'channelsl'connected between ground andthe cathodes bi'saidrectificrs and across which the'commonfr'ectified. voltage of all of said. channels. appears, and; a conn'ecltion. from said common output resistor for sun.- plying a positive bias. toithe cathodesj of; said diodes, whereby the rectified voltage .acrosssaid common. resistor resultingffromfthe strongest signal in. any onechannel, biases the diodes of the other channels. to prevent signal. current, passing throughthelcontrol amplifiers .of said other chan: nels.

3. A diversity.receiving'systemhaving a plurales t- 10 nuts of. said amplifiers, a. common resist r o al1, 0f said rectifiers and' across'which appears the rectified output of said system, and: a connection from said common resistor to, said means for supplying abias of' predetermined polarity to said circuits, whereby the rectified voltage across said common resistor resulting from-thestrongest signalirrone receiver prevents the circuits associated with theother receivers from conditioning their amplifiers to pass signal energy.

4 A diversity receiving. system having a plurality ofreceiversor the superheterodyne type, a common het'erodyne oscillator for all, of saidfreceivers, a balanced alternating current amplifier for each'receiver and' having its input coupled to the intermediate frequency outputof the receiver andarrangedto be non-conductive to signal, energy while in thebalanced condition, a,d io de circuit-coupled-to theinputioi each balanced amplifier and responsive tosignalenergy for upsetting the balanced-condition of; said amplifier and thus enabling said amplifier to pass signal energy, connections between the diode-circuits associated with all of said-receivers, rectifiers coupled tothe difierent' outputs-- oi; said balanced amplifiers, connections between the rectifiers associated with all of said receivers; a common output impedance for said" rectifiers, and a 'connection from, the high'potential side of said common output impedance to 'said' diode circuits yfor biasing, said diodecircuits to the, same. extent so that only that diode circuit to which is supplied the strongestsignal voltage from its associated re ceiverisresponsive. a

5.In' 'a selective system comprising ,arplurality of parallel channels, each havingan amplifier Which'is fed with alternating current signal en.- ergy derived from a differently situated antenna, different diode rectifiers" in parallel to the different inputs or said-amplifiers forcontrolling the responsiveness thereof, a separate resistor in circuit with eachof the diodesof said channels for'building' up a rectified voltage as aresult of the passage of current through the diode in circuit therewith,- means in the, outputs ofsaid channels 'forproducing abias control potential simultaneously applicable to the. different diode rectifiers of said channels for blocking the passage of alternating current signal energies in non-selected channels; said means including a detector stage in the output of each channel and which is connected to correspondingly located detectorsta'ges in the 'otherchannels, and a cornmonloa-d resistor fo'rsaid detector stages, there being a connection from saidcommon load. resis'tor extending back to all of; said diode rec'ti fiersJ '6. In a signalling system subject to. variable transmission conditions, a, plurality or receivers each receiving the same signal and so related to each other that the received signals vary differentlyat "these'veral receivers with variations in transmission conditions; I a common utilization circuit, separate paths extending from said re ceivers to a "common circuit, each of said paths including an amplifier having an input and an o'ut'p'ut,a controlling rectifier coupled to the input of said amplifier, and another rectifierfcollpled to the output of said amplifier, means connecting together'said'last rectifiers and to said common circuit'asaresult of which the, common rectified output of said paths appears in said common circuit,and a connection from said common circuit "to, corresponding electrodes, or said controllin rectinersun' all of said paths t r-sur plying biascontrol potentials thereto to block the passage of signal energy in channels not having the strongest signal.

7. In a diversity receiving system, a plurality of receivers of the superheterodyne type, a common heterodyne oscillator for said receivers, each of said receivers having an intermediate frequency output circuit, separate paths extending from the intermediate frequency output circuits of said receivers to acommon detector circuit, each of said paths including an alternating current amplifier having an input and an output and a controlling rectifier coupled to the input of said amplifier for controlling the responsiveness of said amplifier to the passage of signal energies, there being a connection between corresponding electrodes of the controlling rectifiers of all paths, means coupling said common detector circuit to the outputs of the alternating current amplifiers of all paths, a load impedance for said common detector circuit across which appears the detected output, and a connection from said load impedance for supplying a bias control potential to said controlling rectifiers.

8. In a diversity receiving system for receiving frequency or phase modulated signals, a plurality of receivers of the superhetcrodyne type, each of said receivers having an intermediate frequency output circuit, a common heterodyne oscillator for said receivers, separate paths extending from the intermediate frequency output circuits of said receivers to a common frequency or phase demodulator circuit, each of said paths including an alternating current amplifier having an input andan output and a controlling rectifier coupled to the input of said amplifier, there being a connection between certain corresponding electrodes of the controlling rectifiers of all of said paths, means coupling the outputs of the alternating current amplifiers of said paths to said demodulator circuit, a common detector circuit also coupled to said means, a load impedance for said common detector circuit across which appears the detected output of the intermediate frequency signal energies, and a connection from said load impedance for supplying a bias control potential to said controlling rectifiers.

9. In a diversity receiving system for receiving frequency or phase modulated signals, a plurality of receivers of the superheterodyne type, each of said receivers having an intermediate frequency output circuit, a common heterodyne oscillator for said receivers, separate paths extending from the intermediate frequency output circuits of said receivers to a common frequency or phase demodulator circuit, each of said paths' including an alternating current amplifier having an input and an output and a controlling rectifier coupled to the input of said amplifier, there being a connection between certain corresponding electrodes of the controlling rectifiers of all said paths, electron discharge device means coupling the outputs of the alternating current amplifiers of said paths to said demodulator circuit, a common detector circuit also coupled to said means, a load for said common detector circuit across which appears the detected ouput of the intermediate frequency signal energies,

a connection from said common detector circuit to said controlling rectifiers, and another connection from said common detector circuit to an audio frequency amplifier.

10. In a signalling system subject to variable transmission conditions, a plurality of receivers each receiving the same signal and 50 relat to each other that the received signals vary differently at the several receivers with variations in transmission conditions, a common utilization circuit, separate paths extending from said receiver to a common circuit, each of said paths including an amplifier having an input and an output, a controlling rectifier coupled to the input of said amplifier, and another rectifier coupled to the output of said amplifier, including a first switch connecting together said last rectifiers and to said common circuit as a result of which the common rectified output of said paths appears in said common circuit, a connection including a second switch from said common circuit to corresponding electrodes of said controlling rectifiers in all of said paths for supplying bias control potentials thereto to block the passage of signal energy in channels not having the strongest signal, means for combining the intermediate frequency energies in said paths comprising another amplifier in each path coupled to the output of the first amplifier and connections between the output electrodes of said other amplifiers, a detector for the combined intermediate frequency energies, and means including said second switch for supplying a bias control potential to said controlling rectifiers from the output of, said last detector.

11. A diversity receiving system comprising a plurality of channels coupled to geographically spaced antennas, a balanced amplifier in each channel and having an input and an output, individual rectifiers coupled to the input circuits of said balanced amplifiers, each rectifier being arranged to control the degree of balance and thereby the degree of amplification 0f the balanced amplifier in its particular channel, means for combining and rectifying the outputs of said balanced amplifiers, and means for controlling the degree of rectification of said input rectifiers by said combined and rectified output.

12. A diversity receiving system comprising a plurality of channels coupled to geographically spaced antennas, a balanced amplifier in each channel, said balanced amplifier including a pair of vacuum tubes having input electrodes coupled together in one phase relation and output electrodes coupled together in a relation different from said first phase relation, individual rectifiers coupled to the input circuits of said balanced amplifiers, each rectifier being arranged to control the degree of balance and thereby the degree of amplification of the balanced amplifier in its particular channel, means for combining and rectifying the outputs of said balanced amplifiers, and means for controlling the degree of rectification of said input rectifiers by said combined and rectified output.

13. A diversity receiving system comprising a plurality of channels coupled to geographically spaced antennas, a balanced amplifier in each channel and having an input and an output,,a controlling rectifier in the input circuit of each balanced amplifier and so coupled thereto as to control the degree of balance and thereby the degree of amplification of said amplifier, a pair of amplifier tubes for each channel having their inputs coupled in parallel to the output of the balanced amplifier in that channel, means in each channel for rectifying the output of one of said pair of amplifier tubes therein, means for combining said rectified outputs from all of said channels and for controlling the degree of rectification of said controlling rectifiers by said combined rectified output, and means for combining 13 the outputs of said other tubes of said pairs from all of said channels.

14. A diversity receiving system comprising a plurality of channels coupled to different antennas, an amplifier in each channel and having an input and an output, a controlling rectifier in circuit with the input of each amplifier for controlling the conductivity thereof, a pair of tubes for each channel having their inputs coupled in parallel to the output of the amplifier in that channel, means in each channel for rectifying the output of one of said pair of tubes, means for combining said rectified outputs from all of said channels and for controlling the degree of rectification of said controlling rectifiers by said combined rectified output, and means for combining the outputs of said other tubes of said pairs from all of said channels.

15. In a diversity receiving system, a plurality of receivers of the superheterodyne type, each of said receivers having an intermediate frequency output circuit, separate channels extending from the intermediate output circuits, each of said channels including an alternating current amplifier having an input and an output, a controlling rectifier in circuit with the input of each amplifier for controlling the degree of conductivity thereof, there being a connection between certain corresponding electrodes of the controlling rectifiers of all of said channels, a pair of amplifier tubes for each channel having their inputs coupled in parallel to the output of each amplifier, means in each channel for rectifying the output of one of said pair of tubes thereof, means for combining said rectified outputs from all of said channels and for controlling the degree of rectification of said controlling rectifiers by said combined rectified output, and means for combining the alternating current outputs of said other tubes of said pairs from all of said channels.

16. In a selector system comprising a plurality of parallel channels each having an amplifier which is fed with alternating current signal energy derived from a differently situated antenna, individual rectifiers coupled to the inputs of said amplifiers of said channels for controlling the responsiveness thereof, means in the outputs of said channels for producing a bias control potential and for applying this bias potential simultaneously to the different rectifiers in said channels, to thereby block the passage of alternating current signal energies in non-selected channels, said means including a rectifier in the output of each channel and connections from corresponding electrodes of these rectifiers in the outputs of the channels to corresponding electrodes of the first rectifiers which are coupled to the, inputs of said amplifiers, and a common load resistor for the rectifiers in the outputs of said channels.

1'7. A diversity receiving system having a plurality of receivers coupled to different and spaced antennas, a common heterodyne oscillator coupled to said receivers for enabling said receivers to produce intermediate frequency outputs of the same frequency, separate amplifier stages coupled to the intermediate frequency outputs of said receivers, each of said amplifier stages having a push-push input circuit and a push-pull output circuit, a first rectifier coupled to the push-push input of each of said amplifier stages, means connecting together the cathodes of all of said first rectifiers, a second rectifier coupled to the push-pull output of each of said amplifier stages, each of said rectifiers having a cathode electrode, means connecting together the oathodes of said second rectifiers, a common output resistor for said second rectifiers, and a direct current connection from the high potential terminal of said resistor extending back to the cathodes of said first rectifiers to supply a bias thereto upon the appearance of rectified output voltage across the resistor.

18. A diversity receiving system comprising a plurality of channels coupled to different geographically spaced antennas, each of which includes an amplifier stage having a pair of vacuum tube electrode structures, each of said structures including an input and an output electrode, means connecting said input electrodes cophasal- 1y, means connecting said output electrodes in an out-oi-phase relation, a circuit for developing unidirectional current from the received signal energy and for applying said current to one of said input electrodes, and connections to said structures for maintaining symmetry between said electrode structures, as a result of which no effective output current fiows from said output electrodes in the absence of said unidirectional current, and a common utilization circuit for said channels.

19. A diversity receiving system comprising a plurality of channels coupled to difierent geographically spaced antennas, each of which includes an amplifier stage having a pair of screen grid vacuum tube electrode structures, each of said structures including an input and an output electrode, means connecting said input electrodes cophasally, means connecting said output electrodes in an out-of-phase relation, a circuit for developing unidirectional current from the received signal energy and for applying said current to one of said input electrodes, a potentiometer between the screen grids of said structures, a connection from a source of direct current voltage to a tap on said potentiometer for varying the relative values of the screen grid voltages, and a common utilization circuit for said channels.

20. A diversity receiving system comprising a plurality of channels coupled to different geographically spaced antennas, each of which includes an amplifier stage having a pair of screen grid vacuum tube electrode structures, each of said structures including an input and an output electrode, means connecting saidinput electrodes cophasally, means connecting said output electrodes in an out-of-phase relation, a circuit for developing unidirectional current from the received signal energy and for applying said current to one of said input electrodes, means, for supplying direct current voltages of positive polarity to said screen grids and for varying the values of said voltages to such extent that the amplification of said electrode structures is equal.

MURRAY G. CROSBY.

REFERENCES CITED Name Date Schock June 16, 1942 Number 

